Engineering Manual o.. - HVAC.Amickracing

AIR HANDLING SYSTEM CONTROL APPLICATIONSFEATURES1. Smoke, low temperature, and high static pressure safetyshutdown (hard-wired).2. Optimized start-stop control of supply, return, and exhaustfans.3. Proof of operation interlocking and alarming on supplyand return fans.4. Software on-off-auto system command.5. Zero ventilation/exhaust during preoccupancy operationalperiods.6. May be modified for night purge and prepurge operation.7. After-hours operation function; duration is operatoradjustable.8. Positions valves and dampers properly during off modes.9. Night low temperature operation.10. See Smoke Management Fundamentals section for smokecontrol considerations.CONDITIONS FOR SUCCESSFUL OPERATION1. See REQUIREMENTS FOR EFFECTIVE CONTROL.2. Proper hardware and software interlocks with heating,cooling and terminal equipment.3. To protect the AHU housing and ductwork, the highpressure cutout must be hard-wired and located with aminimum of tubing to prevent delays of operation.Modulating limit control is not recommended since theproblem causing the high pressure is rarely a control loopmalfunction, but a physical one (smoke damper slammingshut, sensor tubing cut or failed, vane actuator linkagefailure, etc.).LIMITATIONS1. Heating and cooling equipment must be available tooperate.2. On large 100% OA systems and systems where OA andRA dampers both close upon fan shutdown, dampersshould be enabled prior to fan start, and the fan shouldstart only after damper end switches prove dampers arein safe positions.SPECIFICATIONSAir handling system shall be under program control, subjectto SA and RA smoke detectors, SA high pressure cut-out, andheating coil leaving air low-temperature limit control; and shallbe subject to system software on-off-auto function.Supply fan shall be started and stopped by an optimum startstopseven day time schedule program, an unoccupied low spacetemperature limit program, or by an occupant via push buttonrequest. The push button shall be integral with the spacetemperature sensor. Any push button request shall provide sixtyminutes (operator adjustable) of full system operation.Return fan shall operate anytime the supply fan proves flow(via a current sensing relay).The exhaust fan shall operate during scheduled occupancyperiods and during occupant requested after-hour periodsanytime the return fan proves flow.Heating/cooling plant (based upon fan system demands),temperature, humidity, pressure, and ventilation controls shallbe enabled to operate anytime the fan system operates. Unlessotherwise specified, during fan off periods, N.O. heating andcooling valves shall position closed, N.C. steam valves shallposition closed, N.C. humidifier valves shall position closed,N.C. outdoor and relief dampers shall position closed, and N.O.RA dampers shall position open.ENGINEERING MANUAL OF AUTOMATIC CONTROL193